Membrane air dryer for vehicle air brake system

ABSTRACT

An air drying system for a vehicle including an membrane air dryer is provided. The air dryer is supplied with a stream of compressed air that has a low and constant concentration of oil vapor. A coalescing filter element may be used to maintain the oil vapor concentration. The filtered material may be discharged from the coalescing filter by a pressure swing drain valve, which discharges the filtered material upon unloading of the compressor.

FIELD OF THE INVENTION

[0001] This application is a continuation-in-part application of U.S.patent application Ser. No. 10/274215 filed on Oct. 18, 2002 forMEMBRANE AIR DRYER AND METHOD OF MOUNTING A MEMBRANE DRYER TO A VEHICLE,the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a vehicle air dryer and morespecifically to a membrane air dryer for a vehicle.

BACKGROUND OF THE INVENTION

[0003] In air brake systems, such as those implemented in commercialtrucks, compressed air from the vehicle compressor is dried prior todelivery to the vehicle brakes and other compressed air operatedcomponents. The compressed air is dried to make the vehicle brakesoperate effectively, and also to prevent damage to the brakes and otherdownstream components. Typically, an air dryer with a desiccant bed isplace between the compressor and the brakes. The desiccant bed air dryerremoves moisture from the compressed air thereby permitting only driedcompressed air to continue downstream to the brakes and othercomponents.

[0004] Several problems exist with desiccant bed air dryers. First, thedesiccant degrades as it becomes contaminated with organic components,such as oil vapor or aerosols, for example. As such, the desiccant bedmust be periodically changed in order to maintain an effective airdryer. Second, desiccant beads have a saturation point, beyond which noadditional moisture can be absorbed. In order to maintain an effectivedesiccant air dryer, a periodic purge of the desiccant is required inorder to keep the desiccant from becoming saturated. In typicaldesiccant bed air dyers, a purge cycle is established when thecompressor unloads, thereby allowing the desiccant to regenerate. Insome situations, the compressor is required to maintain a lengthy cyclebefore it can be unloaded. These situations are somewhat frequent incommercial vehicles, such as during rapid braking and use of ancillaryair powered equipment. During these long compressor cycles, thecompressor charging duration can exceed the desiccant water absorptioncapacity and subsequent wet air can pass downstream to the brake system,or other components, where it can cause damage or other problems.

[0005] While it is known that membrane air dryers can produce a steadystream of dried air without requiring periodic change or periodicpurging, membrane air dryers have generally only been implemented inclean air systems. Contaminants, such as oil aerosols, hinder theperformance of membrane air dryers since the hydrophilic membrane tubesare resistant to organic components. The organic contaminants enter themembrane and foul up the surface of the membrane. This fouling of themembrane by organic contaminants prohibits air from passing through themembrane, thereby reducing the effectiveness of the membrane air dryer.As such, membrane air dyers have not been used in connection withvehicles.

SUMMARY OF THE INVENTION

[0006] An air drying system for a compressed air system of a vehicle isprovided. The system includes a membrane air dryer and a means formaintaining a fairly constant and fairly low oil vapor concentration inthe compressed air system. In one embodiment, a coalescing oil filter isused to maintain the oil vapor concentration below a threshold level.Another embodiment includes a pressure swing drain valve that actuatesupon unloading of the vehicle compressor to discharge the filteredmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The membrane air dryer of the present invention may be morereadily understood by reference to the following drawings. While certainembodiments are shown as illustrative examples of the membrane airdryer, the scope of this application should not be construed as limitedto these illustrative examples.

[0008]FIG. 1 is a cross-sectional side view of a membrane air dryersystem of the present invention;

[0009]FIG. 2 is a cross-sectional side view of a membrane air dryer;

[0010]FIGS. 3A and 3B are close-up cross-sectional views of thedischarge and feed ends of a membrane air dryer; and

[0011]FIG. 4 is a cross-sectional view of the membrane air dryer shownin FIGS. 3A and 3B, wherein the cross-section is taken through A-A.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The vehicle air brake system membrane drying system 10 generallyconsists of a coalescing [Must it be a coalescing filter? If not, whatother types of filters might work? The use of a coalescing filter incombination with the membrane dryer might help the patentability of thebroadest claims, but we may also want to try some other approaches.]filter element 20, a membrane air dryer 30, and a mounting arrangementor means for attaching the membrane air dryer to a vehicle 35. While thedetails of the air brake system membrane drying system 10 are disclosedherein for a preferred embodiment of the invention, one skilled in theart should appreciate that the elements of the membrane drying system10, namely the coalescing filter element 20, a membrane air dryer 30,and a means for attaching the membrane air dryer to a vehicle 35, maytake on a number of different embodiments. It should be understood thatthese additional embodiments are intended to be apart of this inventionto the extent such embodiments fall within the scope of the claims.

[0013] The coalescing filter element 20 may be a single stage coalescingfilter, such as, for example, a Bendix PURAGUARD™. The filter element 20may include a filter housing 40, a pressure swing drain valve 42, suchas, for example, Bendix DV-2, and a restriction orifice 44 within thefilter element housing 40. As shown in FIG. 1, air from a compressorenters through orifice 46 and then is forced through the filter element20. Air exists the filter element 20, greatly reduced in oil vapor andaerosol concentration into filter space 48 prior to exiting the filterthrough exit port 50.

[0014] A pressure swing drain valve 42 may be attached to the lowerportion of the filter element housing 40, thereby taking advantage ofgravitational forces to assist in the collection of condensed fluids orheavier gases. One skilled in the art should appreciate that thepressure swing drain valve 42 may be located in other locations along orabout the filter housing. Furthermore, the pressure swing drain valvemay be integral with the filter housing, or attached as a separate unit.Additionally, the drain valve does not need to be pressure swing driven,and thus may be actuated by any other means, such as, for example, amanual drain valve or time-release drain valve. However, the use of apressure swing drain valve is preferred since each time the compressorunloads, or stops compressing air, pressure from the discharge linefalls thereby activating the pressure swing drain valve 42 which expelsliquid water and/or oil from the brake system. At the connection betweenthe pressure swing drain valve 42 and the filter space 48, a restrictionorifice 44, or some other means for restricting air flow, may be placedin order to prevent pressure pulses from the compressor from activatingthe pressure swing drain valve 42 with each piston stroke. An orifice ofabout 0.046 inches is preferred.

[0015] The use of a coalescing filter 20 has been determined tofacilitate in the drying of the compressed air by the membrane air dryer30. A coalescing filter, such as the Bendix PURAGUARD™ has thecapability to maintaining the oil vapor and oil aerosol concentration inthe compressed air stream at a fairly consistent level. Unlikeconventional desiccant dryers which continue to degrade with eachexposure to contaminants, such as oil vapor, a membrane air dryer willcontinue to produce approximately the same results as long as the oilvapor concentration is maintained at a fairly constant level below athreshold level, which is defined by the desired air drying results.Since the membrane air dryer is typically composed of hydrophilicelements, organic compounds, such as oil, builds up on the surface ofthe membrane. At a given concentration, the air passing over the oilcondensed on the surface of the membrane will push the oil through themembrane, thereby freeing the membrane for drying. As such, there is anequilibrium concentration of oil wherein the air drying capability ofthe membrane is fairly constant. The coalescing filter element 20 isused to maintain the concentration of oil vapor at an equilibrium levelthat will produce air of a predetermined dryness. Additionally, thecoalescing filter 20 may reduce the concentration of water vapor in thecompressed air stream, thereby reducing the load on the membrane airdryer 30. [Is there data available or some estimated range of acceptableoil vapor concentration? Or data ranges dependent on size (surface area)of the membrane?]

[0016] Filtered air leaves the filter element 20 through exit port 50and passes to the membrane air dryer 30 through the supply port 60located in the supply end cap 62. The compressed air, after travelingthrough the plurality of membrane air dryer hollow fibers 64, as shownin FIG. 4, is now dry and collected in the delivery volume 66 located inthe delivery end cap 68. The dried compressed air in the delivery volume66 is either fed through the membrane air dryer core 70 as backflow, orthrough a delivery check valve 72 to the air supply tanks, brakes, orother downstream components. The backflow travels along the outside ofthe membrane air dryer fibers 64, collects the water vapor and vents tothe atmosphere through vent holes 74. Preferably, the portion of airthat is used as backflow is between about 15 and 20 percent of the totaldried air flow. In the embodiment shown in FIG. 3A, a metering orifice76 is used to control the backflow rate.

[0017] Materials suitable to achieve the desired membrane morphologyinclude those polymeric materials typically known for use in makingpermeable membranes exhibiting the specified morphology. Examples of thepolymeric materials from which the hollow fibers are formed include, butare not limited to, polysulfones, polyethersulfones, polyarylsulfones,polycarbonates, nylons, polyimides, polyvinylidenedifluorides,polyvinylidenedichlorides, cellulosics, polyacrylonitriles, and othersknown to make permeable membranes, used alone or in combination.Inorganic materials capable of forming an appropriate membrane structuremay also be suitable. Examples of such inorganic materials include, butare not limited to, ANOPORE® membranes, which are anodic aluminum oxideflat sheet membranes. ANOPORE® membranes are commercially available fromWhatman, Inc. in Clifton, N.J. Other suitable flat sheet membranes mayalso be used. The desired morphology may be achieved with the suggestedmaterials by a number of processing and formation techniques, among themphase inversion, thermal induced phase separation (TIPS), track-etching,or other known or envisioned means of fabricating permeable membraneswith appropriate selective permeability. Further suitable membranes aredisclosed in U.S. Pat. Nos. 5,525,143 and 6,083,297, each of which isincorporated herein by reference in its entirety.

[0018] The means for attaching the membrane air dryer 35 to a vehiclecan take on a number of embodiments, such as, for example mounting bolts78 through the vehicle frame 80 as shown in FIG. 1. Further mountingarrangements are disclosed in commonly-owned co-pending U.S. applicationSer. No. 10/274215. Such mounting arrangements may also be dictated bythe structure of the coalescing filter 20 and membrane air dryer 30,such as an embodiment wherein the coalescing filter 20 and membrane airdryer 30 are integral.

[0019] It will be appreciated that the membrane air dryer assembly cantake the form of various configurations and mounting arrangements. Itshould be further understood that the membrane air dryer andcorresponding end caps can be used either with new equipment, orretrofit to attach to existing components. Such existing components maycause minor alternations to the design of the membrane air dryer;however one skilled in the art should appreciate that these minormodifications fall within the scope of this application. This inventionis intended to include such modifications and alterations in so far asthey fall within the scope of the appended claims or the equivalentsthereof.

1. An air drying system for a compressed air system of a vehicle,comprising: a coalescing filter element located downstream from avehicle compressor, wherein said coalescing filter element is disposedwithin a coalescing filter housing; and a membrane air dryer attachableto the vehicle, wherein said membrane air dryer receives a compressedair stream from said coalescing filter element.
 2. The air drying systemof claim 1, wherein said coalescing filter element maintains a fairlyconstant oil vapor concentration in the compressed air stream.
 3. Theair drying system of claim 1 further comprising a pressure swing drainvalve attached to said coalescing filter housing, wherein said pressureswing drain valve discharges filtered material from said coalescingfilter element when there is a pressure swing within the coalescingfilter housing.
 4. The air drying system of claim 3, wherein saidpressure swing drain valve is actuated each time the compressor unloads.5. The air drying system of claim 3, wherein said pressure swing drainvalve includes a restriction orifice.
 6. The air drying system of claim5, wherein said restriction orifice is between about 0.04 inches andabout 0.06 inches.
 7. The air drying system of claim 1, wherein saidmembrane air dryer comprises a supply end cap, a membrane air dryercore, and a delivery end cap, wherein said membrane air dryer coreincludes a plurality of hollow fiber membrane tubes.
 8. The air dryingsystem of claim 7, wherein said membrane air dryer further comprises ametering orifice for creating a backflow of air through said membraneair dryer core.
 9. The air drying system of claim 8, wherein saidmetering orifice allows between about 15 and about 20 percent of thecompressed air stream exiting said plurality of hollow fiber membrane toflow back through said membrane air dryer core.
 10. The air dryingsystem of claim 7 further comprising a check valve disposed within saiddelivery end cap, said check valve regulating the flow of the compressedair stream between the membrane air dryer and one or more downstreamcomponents.
 11. An air dryer for a compressed air system of a vehicle,comprising a membrane air dryer which receives a compressed air streamfrom a compressor, wherein said membrane dryer includes a supply endcap, a membrane air dryer core, and a delivery end cap, wherein saidmembrane air dryer core includes a plurality of hollow fiber membranetubes.
 12. An air drying system for a compressed air system of avehicle, comprising a membrane air dryer which receives a compressed airstream from a compressor, and a means for maintaining a fairly constantand fairly low oil vapor concentration in said compressed air stream.13. The air drying system of claim 12, wherein said means formaintaining a fairly constant and fairly low oil vapor concentration insaid compressed air stream is a coalescing filter element disposedwithin a filter housing located upstream from said membrane air dryer.14. The air drying system of claim 13, wherein said coalescing filterhousing includes a drain valve.
 15. The air drying system of claim 14,wherein said drain valve is actuated by changes in the pressure withinthe filter housing.
 16. A method of drying a compressed air stream on avehicle, comprising the steps of: supplying the compressed air stream toa coalescing filter element, wherein said coalescing filter element isdisposed within a filter housing; filtering the compressed air streamwith said coalescing filter element; supplying the compressed air streamto a membrane air dryer; drying said compressed air stream; anddelivered the dried compressed air stream to one or more downstreamcomponents.
 17. The method of claim 16, further comprising the step ofdraining filtered material from said filter housing.
 18. The method ofclaim 17, wherein the step of draining filtered material from saidfilter housing is preformed by a pressure swing drain valve.
 19. Amethod of drying a compressed air stream on a vehicle, comprising thesteps of: maintaining an oil vapor concentration in the compressed airstream below a predetermined threshold level; supplying the compressedair stream to a membrane air dryer; and drying the compressed airstream.
 20. The method of claim 19, wherein the means for maintaining afairly constant and fairly low oil vapor concentration in the compressedair stream is a coalescing filter element disposed within a filterhousing located upstream from said membrane air dryer.
 21. A system fordrying air in a compressed air system of a commercial vehiclecomprising: an air compressor; a coalescing filter element locateddownstream from said compressor, wherein said coalescing filter elementis disposed within a coalescing filter housing; a membrane air dryerattachable to the vehicle, wherein said membrane air dryer receives acompressed air stream from said coalescing filter element; and a brakesystem, wherein said brake system receives dried air from said membraneair dryer.
 22. An air drying system for a compressed air system of avehicle, comprising: a means for maintaining an oil concentration in thecompressed air system below a predetermined threshold level; and amembrane air dryer attachable to the vehicle, wherein said membrane airdryer receives a compressed air stream from said coalescing filterelement.